A small amount of fertilising agents, especially calcium phosphate, it is used as manure on the neighbouring fields. On the occasion of a visit some years ago to the works of M. Lair at Bondy, there were four sets of the above apparatus in existence, capable of treating 200 cm. of eau vanne per twenty-four hours. The liquors which were under treatment at that time contained only 25 grms. of ammoniacal nitrogen per litre; they yielded 114 kilos, of ammonium sulphate per cubic metre, and required the combustion of 18 kilo, of coal per kilo, of sulphate obtained. The liquors which were run off contained only 006 to 01 grm. of nitrogen per litre. Even with these unfavourable conditions, crystallised ammonium sulphate was obtained directly in the saturation vats, a result due to the slow speed of the operation, and to the presence of free ammonia in the mixture, which, being itself very volatile, assists in carrying off the ammonium carbonate. This apparatus presents several important improvements on the preceding, both from the point of view of public health and that of the manufacture of ammonium sulphate. An objection to it is however, that it treats a comparatively small quantity of the eau vanne, and that the column requires frequent cleaning to remove the deposits produced by the lime. 4. The Apparattts of Sintier and Muhe, — MM. Sintier and Muhe have made valuable modifications in certain portions of the preceding apparatus. These modifications produce no change in the course of the operations, but allow a more perfect result to be obtained. They consist essentially in the combination of the mud tank and the exchange heater into one vessel, and in a different method of using the lime intended for setting free the ammonia of the fixed salts. In Lair's apparatus the mud tank and the heater are distinct, a consequence of which is that the liquors from the column are much cooled by the surrounding air before they arrive at the heater ; and further, the mud carries away heat which cannot be recovered. The combined mud tank and heater of Sintier and Muh^ is intended to remedy these two defects. It consists of two tubular vessels (A and B, Fig. 5). The first A, which is a heater resembling that of Lair, consists of a wrought-iron cylinder containing a group of tubes which connect the upper and lower parts. The second, B, consists of four portions — (1) The lower chamber under the plate, which carries the tubes ; (2) a cylindrical vessel of wrought iron, supporting a cone, 6, the apex of which is connected with a bent tube ending outside in a stop-cock, s, for drawing off the deposit ; (3) a second cylindrical vessel resting on the base of the cone, and open above for the removal of the mud which collects round the tubes ; (4) a small upper receiver, connected with the lower chamber by a group of 25 to 30 tubes. This receiver is fixed above the cylinder B, so as not to be in the way when cleaning the tubes. The eaux vannes delivered by the pump P pass through the tubes of the heater A, issue by the pipe /, and rise in the tubes of the vessel B, passing finally by the pipe C into the column. During this transit they acquire heat from the exhausted liquors which travel in the opposite direction. These latter descend by the syphon-pipe e, e, enter the cylinder 'p at /'j flow over the cone &, enter the heater A at A, and escape by the pipe K completely cooled. The level at which the exhausted liquors stand in the heater B, is such that the cylindrical portion d! is always about four-fifths full. The quantity of liquid contained in this portion is equal to that on the plates. We have seen above that the introduction of lime into the column produces numerous obstructions, necessitating frequent cleaning. MM. Sintier and Muh6 have completely remedied this inconvenience by greatly augmenting the capacity of the first chamber (d) of the column, into which the steam is admitted by the stop-cock V, and it is into this portion of the apparatus that the lime is injected by the pump p, which draws it from the mixer 0. The lime is intimately mixed with the liquor by a stirrer, which is shown in dotted lines. The fixed ammoniacal salts are thus decomposed without fear of choking the apparatus. The vapours from the column are passed into sulphuric acid in the lead-lined vat. 5. Bilange's Apparattts. — As stated in Chap. II. § 1, M. Bilange has sought to solve the double problem of producing a manure of immediate utility to agriculture, and of not allowing the escape, either into the air or the waste liquors, of any but inodorous and imputrescible substances. We have described the first part of his process, that is to say, the separation of the crude eaux vannes and the production of filter-press cakes; it remains to describe the process of distilling the clear liquor for the extraction of the ammonia. The distillation is performed at reduced pressure, so as to lower the boiling point of the liquid considerably, and thus diminish the effluvium which would still result from the treatment of these clarified liquors. The arrangement adopted strongly resembles that in use in sugar works for concentrating the juice. It consists of four vertical tubular drums, closed air-tight, and heated by steam from a boiler. In these vessels the ammoniacal liquors are raised to a temperature of only 60 to 65°, which is sufficient to cause them to part with the ammonia they contain, in consequence of diminished pressure, which is produced by a pump working during the whole operation. The ammoniacal vapours given off from the heaters pass into a closed chest connected with the air-pump. In this lead-lined chest the mother liquors of a previous operation are placed, and from time to time sulphuric acid is admitted. Samples of the liquor drawn from the chest show when the addition of more acid is needed. Only small quantities can be introduced at one time, lest the action should be too violent. The ammoniacal vapours, before reaching the sulphuric acid, are passed through a weak solution of ammonium sulphate in an intermediate vessel. This scrubber, which acts as a safety vessel, can, in case of repairs being needed, take the place of the neutralising vessel. When it is judged that sufficient salt has been formed, the addition of sulphuric acid is discontinued and the solution of sulphate is evaporated, steam being introduced into a coil lying on the bottom of the vessel, and connection being made with the vacuum chamber. Evaporation takes place very rapidly, and must not be pushed too far, lest the whole mass should solidify and need to be redissolved. When the liquor is sufficiently concentrated, it is allowed to run out into a crystalliser placed below. For this purpose the supply of steam to the coil is shut off, communication with the vacuum apparatus is closed, and air is allowed to enter ; the hot liquor is then allowed to run out, and it crystallises on cooling. The salt is fished out as it crystallises, and is drained and dried. It is evident that this process avoids the production of the noxious vapours which result from the use of distillation columns, and which it has not been found possible to prevent on the large scale. In our opinion, the only objection to this process is that it requires a very costly plant, which must wear out very quickly. Nevertheless, a somewhat long experience at Bondy has proved the efficiency of this process, which satisfies public hygiene, and would prevent the accumulation of pasty matters. 6. The Kuentz Process. — M. Kuentz has suggested a special method of treatment of the eaux vannes to avoid the escape of noxious products, which of late years, and especially in Paris, has given rise to so many complaints. The vapours from the distillation columns are usually, as we have seen, passed into sulphuric acid of 53°, in which the ammonia is converted into sulphate, whilst the carbonic and hydrosulphuric acids, with the vapour of water and the offensive gases which accompany them, are sent into the chimney of the works, or better through a furnace. Under these conditions the offensive gases are diluted with a large volume of carbonic acid arising from the decomposition of the ammonium carbonate, which prevents the complete destruction of these gases by heat and oxygen. After cooling, the gaseous mixture diffuses through the air, and the effluvia, wafted by the wind, reach the earth at a greater or less distance from the works. To destroy these vapours, Kuentz has proposed to absorb the carbonic and sulphydric acids by lime, which would render the destruction of the odorous vapours, by passing them through a special coke furnace, easy and complete. It was pointed out by M. Girard that these vapours might be destroyed by passing them over glowing coke. But these fumes, in the condition in which they issue from the apparatus, being rich in carbonic acid, are incombustible, and are only destroyed with difficulty. Kuentz's process, whilst solving the problem completely, requires a large amount of lime. Kuentz has therefore proposed, as a means of rendering the operations more easy and complete, to acidify the vapours in closed vessels, and by double decomposition to retain most, if not all, of the carbonic acid; the uncondensable gases can then be passed through a furnace and completely destroyed. The following is the process for obtaining the ammonium sulphate : — Phosphate of lime is treated with dilute sulphuric acid to set free all the phosphoric acid ; the phosphoric acid obtained is neutralised by strong ammoniacal liquors, prepared as we shall see further on. Ammonium phosphate is thus obtained, which is evaporated. The calcium sulphate, obtained in the treatment of the phosphate of lime by sulphuric acid, being treated with concentrated ammoniacal liquors, or by the gases from the column, yields ammonium sulphate, which remains in solution, and calcium carbonate, which precipitates or is separated by filtration. Operating thus, there is no disengagement of carbonic acid ; the neutralisation and evaporation of the liquors takes place in closed vessels, and the uncondensable gases which issue from the apparatus are passed through scrubbers containing lime and oxide of iron, and then through a special furnace, where they are destroyed. This process is somewhat long, but is very reasonable. 7. Process and Apparatus of Hennehutte and Vaur4al.^^The process is worked by the Soci^te anonyme des produits chimiques du Sud-Ouest. It consists in treating the entire sewage with 2 to 3 thousandths of zinc sulphate and 5 thousandths of aluminium sulphate, then allowing the mixture to settle, and running off the clear liquor, which is sent to the ammonia stills. The deposit is treated with a further quantity of the same chemicals, then forced into filter presses by compressed air. In this way very firm filter-press cakes are obtained, which are easily dried by simple exposure to air or in stoves, and clear filtrates, which are added to the former. By the use of the sulphates of zinc and alumina the liquors are desulphurised, and the alumina precipitate assists the separation of the solids. The dried cakes contain 3 to 4 per cent, of nitrogen and 3 per cent, of phosphoric acid. The apparatus devised by Hennebutte and Vaureal is shown in Fig. 6 ; it consists of three rectangular boilers. A, B, C, of cast iron, forming one chamber, and arranged so as to give a continuous fall. The boilers B and C contain vertical partitions h and c, which are fixed 01 m. from the bottom, so as to force the vapours from the lower boilers A and B to bubble through the contents of B and C, and keep them agitated. At the upper part of the apparatus there is a rectangular vat D, containing a condenser formed by an oval wrought-iron tube E, connected with the boiler C by a wide tube e. The pipe F, which is the outlet of this condenser, carries a valve /, which allows a partial vacuum to be maintained in the apparatus. This pipe is connected with a chest G, for the reception of the condensed liquids, or to pass them at pleasure into another chest H, which is heated by the boiler A, the top of which forms the bottom of H ; a pipe with stop-cock allows H to be emptied into B. Lastly, the pipes g and h allow the ammoniacal gases to pass into a sulphuric acid vat, where they are retained as sulphate. The wrought-iron tank K is intended to receive the exhausted liquors issuing from the last boiler, and the tank L, which is fed with the hot liquors run off, contains a series of iron pipes through which the fresh eau vanne circulates, and where it becomes heated before entering the measuring vat M, and then the boiler C. The apparatus works in the following manner : — The crude eau vanne, arriving from an upper reservoir, fills the chamber D of the condenser ; it then runs down by the pipe d into the system of tubes in the tank L containing the hot exhausted liquors, and becomes heated to about 80°. It then rises by the pipe m into the measuring vat M, which is connected by a wide stop-cock with the boiler C. Thence it passes into that boiler, where it reaches about 90*”. In this boiler it parts with most of its volatile ammonia, which is driven off by the current of mixed vapours arriving from the other boilers. The ammoniacal vapours pass into the condenser, where they are cooled, and by thus diminishing in volume produce a partial vacuum in the apparatus, which permits the liquid in the boiler C to boil at 90°. When the liquid in the lower boiler A is exhausted, it is run into the settling tank K, that from B takes its place in A, the liquid from passes into B, and C receives a charge of fresh eau vanne. Slaked lime is introduced into A by a plug-hole N, which serves at the same time as a safety-valve. The proportion of lime added should be sufficient to decompose all the fixed salts existing naturally in the eau vanne or resulting from the sulphates of zinc and alumina introduced. When the boilers are thus filled, a new operation is commenced. The apparatus is heated by a steam jet introduced into A. The vapours from that boiler pass successively through the liquids contained in the two others, which thus become methodically deprived of their ammonia. The liquids condensed in the cooler are very rich in ammonia and ammonium carbonate ; they are collected in the vessel G, then flow into H, whilst the ammoniacal vapours pass by the pipe g to the acid vat. The concentrated solution in H becomes heated by its contact with A, and gives up the greater part of its ammonia, which passes off by the pipe h to condense in the sulphuric acid. An apparatus of this kind has been fitted up at Villejuif , near Paris. Another is at work at Fribourg en Brisgau (Baden), and treats 25 cm. of eau vanne per twenty-four hours, producing crystallised ammonium sulphate in the neutralising vat.
Key Takeaways
- The Sintier and Muhe apparatus improved on Lair's design by combining mud tanks and heaters, reducing cooling losses and preventing lime deposits.
- Bilange’s process used distillation under reduced pressure to extract ammonia from clarified sewage without producing noxious vapors.
- Kuentz's method involved absorbing carbonic and sulphydric acids with lime before passing the gases through a furnace for complete destruction.
Practical Tips
- Utilize combined heating systems in apparatus designs to reduce cooling losses and improve efficiency.
- Implement reduced pressure distillation techniques to minimize effluvium during ammonia extraction from clarified sewage.
- Use lime or other absorbents to neutralize harmful gases before releasing them into the atmosphere.
Warnings & Risks
- Frequent cleaning of equipment is required in some processes, which can be time-consuming and labor-intensive.
- The use of large amounts of lime in Kuentz's process may lead to significant costs and environmental concerns.
- Proper handling of concentrated solutions and vapors is essential to prevent accidents.
Modern Application
While the specific apparatus designs described are outdated, the principles of efficient resource recovery from waste streams remain relevant. Modern techniques have improved on these historical methods by incorporating automation, safety measures, and more sustainable practices. Understanding these early processes can provide valuable insights into developing innovative solutions for contemporary waste management challenges.
Frequently Asked Questions
Q: What is the primary purpose of using reduced pressure distillation in sewage treatment?
Reduced pressure distillation is used to lower the boiling point of liquid ammonia, allowing it to be extracted from clarified sewage without producing noxious vapors. This method helps in maintaining public hygiene and preventing the release of harmful gases into the atmosphere.
Q: How does Kuentz's process address the issue of escaping odorous gases during sewage treatment?
Kuentz's process addresses this by absorbing carbonic and sulphydric acids with lime before passing the gases through a special furnace for complete destruction. This ensures that no offensive vapors are released into the environment, solving the problem of complaints from nearby residents.
Q: What is the significance of combining mud tanks and heaters in Sintier and Muhe's apparatus?
Combining mud tanks and heaters in Sintier and Muhe's apparatus reduces cooling losses by ensuring that liquors are heated before they reach the heater. This also prevents lime deposits from carrying away heat, improving overall efficiency.